Milk products on which the herding families rely have almost disappeared as cattle die or stop lactating. Mothers are being forced to feed their babies on rice water.

Without horses to ride, pregnant women about to give birth have to walk miles to hospitals which lack essential equipment. Fuel for the few ambulances must be paid for.

An emergency report from the UN disaster management team (UNDMT) says: "For most people in the affected areas, their animals are the only sources of food, transport, heating materials and purchasing power, and the access to medical services and children's education."

"All the horses disappeared during the first heavy snowfall and no one has been able to find them," reports a UN technical adviser, Damien Wohlfahrt, from Dundgobi, where entire herds have been wiped out

"Pneumonia cases are reported to be increasing," says the report. "The influenza pandemic reached Mongolia in late January ... (and) has been spreading rapidly."

Schools have stayed shut because children cannot get to classes or because their families are trekking long distances in search of fresh pasture. Other children are left behind with a grandparent - as many as 12 in the charge of one elderly adult. Experts have long warned that the crisis was waiting to happen, in a country where post-communist economic reforms worsened the position of Mongolia's already numerous poor.

"The current food emergency follows several years in which nutritional standards have been falling ... as the economy has been reoriented from one which was centrally planned to one which is market driven," said the UN Food and Agriculture Organisation (FAO) at the weekend.

"Those most affected by poverty and food insecurity include the unemployed, the elderly, female headed households, pensioners and small herders," it said.

Welfare and health schemes run by the state have collapsed, and teachers are forced to raise their herds to supplement meagre incomes.

The former collective herds were split up into private companies which were frequently monopolised by local leaders, leaving most people worse off. With no controls on competition, herds have been expanded and pastures over-grazed.

Up to a quarter of Mongolia's population of 2.7m people are at risk, said the FAO. Most Mongolian households have fewer than 100 animals, which places them on the brink of poverty and unable to cope with a sudden loss.

The US ambassador in Ulan Bator, Alphonse La Porta, warns that "the human suffering will grow exponentially and there will be significant numbers of people at risk into next winter."

Temperatures fell during the winter 5 to 10C below the average: the lowest recorded was -46C. A drought last summer had already reduced the over-stretched pasture lands.

By December 1.4m registered livestock were recorded dead out of 33.5m, while another 2.2m had been forced to migrate in search of food.

The livestock mortality rate will increase during the spring when snowfalls and dust-storms are common and the grass has not yet grown. The UNDMT says: "In their ill-fed condition, many female small animals and their young are expected to perish."

Mongolia in brief: Blue sky, tough lives

 The Mongolian People's Republic, declared on 26 November 1924, was the world's second communist country

 Three times the size of France, a third of it is covered by the Gobi desert. It has an average elevation of 1580m (about 5,300ft)

 Home to famed takhi horses which Genghis Khan used in his wars of conquest

 Has more than 260 sunny days a year, but long, harsh winters

 Most of the population is nomadic, living in yurts, large round felt-roofed tents. Main industries are copper, livestock, cashmere and wool

 There is an old Mongolian saying: "Breakfast for yourself; lunch, share with your friends; dinner, give to your enemies"